Progress in Laser Desorption Mass Spectrometry: Sample Analysis in the Lab and in Space

W. B. Brinckerhoff, C. M. Corrigan, A. L. Ganesan, T. J. Cornish, P. R. MahaffyGoddard Center for Astrobiology Team Meeting, March 23-24, 2006

Progress in Laser Desorption Mass Spectrometry: Sample Analysis in the Lab and in Space

Theme IV: Analytical Approaches


Outline

1.Theme IV Objectives

2.Methods and Instrumentation

3.Example Analyses

4.What’s Next


Theme IV Objectives

1. Develop new techniques to study the composition of complex planetary materials and analogs in situ APL: Optimize LDMS-based methods for organic analysis that are

complementary to GC/LC-MS, for both lab and spacecraft use

2. Relate the composition of comets and carbonaceous asteroids, via sample analysis, to the organics found in the ISM and those thought to be “pre-biotic.” APL: Utilize capability of laser desorption to examine nonvolatile

organics and other species with little or no sample preparation

3. How can we best study primitive organic-bearing bodies over variable spatial scales and chemical properties? APL: Understand in particular the importance of analyses of complex

(high m.w.), non-volatile phases, at fine spatial scales, to astrobiology


Methods and Instrumentation (APL)

Impact Plasma Chemistry: Exobiology

Laser Mass Spectrometry

LD/LA TOF-MS

Organic Analysis and Method Development:

NAI

AP-MALDI Ion Trap MS

Instrument Development:

PIDDP etc.

LD/LA EPI-TOF-MS

REMPI, RIMS

In Situ Experiments

?

Higher TRL Lower TRL


Methods and Instrumentation (APL)

In situ applications:• Strong mass, power, and complexity drivers LDI• Use the simplest version of an experiment that addresses

specific, high-priority measurement objectives

Laboratory applications:

• Essentially the same “simple” TOF-MS with enhanced laser, imaging, ion optical, sample manipulation, and electronics systems, is a state-of-the-art instrument

• High precision (few m) XYZ manipulation of intact meteorite chips• LD of neutrals (from 10-100 m spots) with selectable • Selectable direct LD ions or fully resonant L2PI, into TOF-MS• Or, LD neutral gas into LC- or GC-MS (Themes 3 and 4)

• Potential to obtain spatially-correlated elemental, isotopic, and organic composition from unprepared samples


Miniature LD-TOF-MS

• Laser TOF-MS can be miniaturized without major performance degradation compared with laboratory instruments.

• Gridless ion optics, low-noise detectors, and nonlinear “ideal” reflectrons permit high mass resolution and low detection limits.

• Caveat: measures mass only (not structure)!

The reflectron corrects TOF dispersion: ions with same m/z but different energies arrive at the detector simultaneously. A nonlinear reflectron focuses LA and LD ions (wide KE band) as well as organic product ions.


LAMS

• LAMS = laser ablation mass spectrometer

• Elemental/ isotopic analysis from stand-off position (airless body: ~ 1 cm – 1 m range)

• Nd:YAG laser ( = 1064 nm, > 1 GW cm-2)

• Sample at electrical ground

• No sample preparation or contact needed

• Elemental LODs as low as ppmw bulk

• Probe on fine scales (spot size 30-100 m) can probe inclusions and detect grains

• Complementary to Pyr-GC/MSm/z (amu/e)

10 15 20 25 30 35 40 45 50 55 60 65 70

0

50

100

150

10 15 20 25 30 35 40 45 50 55 60 65 70

0

50

100

150

0

50

100

150

12C

16O

23Na

24Mg28Si

32S

40Ca

52Cr(Mg2+)

(a) ALH83100

(b) ALH83100

(c) Allende

54Fe

56Fe

58Fe+58Ni

60Ni


DS-TOF• 355 or 337 nm pulses < 108 W cm-2 (1 - 20 Hz)• Unprepared chips or powders, mounted on insertion

probe and held at +5 kV• Monolithic nonlinear reflectron• Double-sided detector system• Organic and elemental analysis capabilities• Refractory organic LODs in low ppbw range• Probe on fine scales (spot size <100 m)

Bold = detected m/z; Non-bold = inferred m/z


“Tower” TOF

• Normal incidence desorption at 266 nm (or 355, 1064, or 337 nm)

• Lateral postionization at 235 – 390 nm with doubled visible OPO

• Unprepared samples mounted on XYZ bellows stage with 13 mm lateral and 25 mm vertical travel

• Instrument and samples are vertical• Samples at electrical ground; flight

tube biased to negative voltage• No pre- or post-acceleration grids• Sensor about 50% size of DS-TOF• Elemental and organic chemical

imaging at resolutions ~ 50 m• Under development!

laser focus pointion extraction lens

detector assembly

ion reflectron

~ 7.5 cm


Sample Handling and Preparation

1st order attitude:

“We don’t need no stinking sample preparation!”

Intact chips: analysis of heterogeneity and association of detected organics with their formation environment. Strongly limited by low concentrations and matrix effects!

Powder samples pressed into probe tip wells. Samples must be inspected for homogeneity given small laser spot size!

2 mm Green River Shale

50 m laser diam.JSC Mars-1

1 mm

ALH 83100

Rocks Fine Powders



• Crushing and sieving: distinguish any real compositional biases from instrument biases (absorptivity dependence)

• Thin, flat samples (e.g. H2O slurry droplet) generally give best resolution and reproducibilty (E-field uniformity?)

Ground and pipetted samples for “bulk” analysis. Surface types (bare metal, tapes, Si slides, and MCP chips) have various advantages for LDMS. <150 mbulk

Palisades Basalt

2nd order attitude:

“Uh, we’d better measure sample-specific effects.”



“How do we get the fine-grained stuff where we want it?”

A compact sample acquisition system for fines uses grooves laser-etched in Si to entrap particles in a pre-defined series of size bins below ~500 m.

50 mlaser diam.


“Simple” Samples - Sand

Na

K

CrFe

SRM 81a SandRLE 200

Li Na K Cr

FeRb

Cs

SRM 81a SandRLE 385


“Simple” Samples – Lithium

• Light (6, 7 amu) alkali metal – RIMS ~ 15%

• High mobility, diffusivity

• Elevated 7Li of CI chondrites may indicate aqueous parent body processing1

• Li gradients and high 7Li could be tracers of major crustal water movement in the source regions of basaltic shergottites2

• Lithium is highly heterogenous in martian meteorites and zoned in pyroxene grains (degassing indicator?)3,4

1. McDonough et al. LPS 2006

2. Reynolds et al. LPS 2006

3. Lentz et al. GCA 2001

4. Herd et al. GCA 2005


• Preliminary UV LDMS data indicate “large” signatures might be recovered from unprepared samples (without matrix)

• We are characterizing the small instrument bias as a function of sample mounting scheme (probe and material details)

• Average of 3 spots and 3 laser pulse energies: • 6Li/7Li = 0.085 compared with LSVEC standard value of 0.0832• Insufficient statistics to determine precision, as yet• A work in progress … may need improved LDI characteristics

6Li/7Li in a Li2CO3 Standard RM 8545 LSVEC

-3.00E-04

2.00E-04

7.00E-04

1.20E-03

1.70E-03

0 1 2 3 4 5 6 7 8 9 10

m/z

SRM 8545 LSVECRLE 70

-5.00E-04

1.50E-03

3.50E-03

5.50E-03

7.50E-03

9.50E-03

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200

m/z

SRM 8545 LSVECRLE 130


“Simple” Samples – Sand + Phenanthrene

-0.0005

0

0.0005

0.001

0.0015

0.002

0 50 100 150 200 250 300

m/z

SRM 81a +0.1% phenanthrene RLE 223

m/z 178C14H10

Rb

Na

Al

X


“Simple” Samples – Sand + Benzoic Acid

Na

Al

K

Ti

CrFe

TiO

Ni

Li TiO2

Rb

C6H5CO

ONa

Ti3FeOC6

Ti2O2

C6H5CO

Na

C10H8

SRM 81a Sand + Benzoic AcidRLE 180

m/z

-0.0005

0

0.0005

0.001

0.0015

0.002

0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400 420 440 460 480 500

SRM 81a Sand + Benzoic AcidRLE 180

Trace hydrocarbon impurities in C6H5COOH as provided (99.5%)

m/z


“Real” Samples – Green River Shale

• Less evidence of extensive high mass aromatics, compared to C-chondrites, consistent with n-alkane dominated IOM from algal source (Greenwood et al. 2004)

• Chemical noise is currently limiting resolution of high-mass parent compounds in powder sample; extensive fragmentation at higher laser power lower P and

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

0.045

0.05

50 100 150 200 250 300 350 400 450 500 550 600

m/z

Green River Shale RLE 200


“Real” Samples – Mars Analogs

4 5 6 7 8 9 10 11 12 13 14 15

0

2

4

6

6Li

7Li (a) Atacama Yungay

0

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0.008

0.009

0.01

50 100 150 200 250 300 350 400 450 500

m/z

Palisades basalt (bulk)RLE 175

-0.005

-0.0045

-0.004

-0.0035

-0.003

-0.0025

-0.002

-0.0015

-0.001

-0.0005

0

150 200 250 300 350 400 450 500

HWMK979 040606 014.6/-0.4/1.8//5/-5.25 kVSA 502RLE 245

435 = 396+39K+

419 = 396+23Na+

321 = 282+39K+

217=178+39K+

305 = 282+23Na+

201=178+23Na+

HWMK979

1 mm


What’s Next?

• DS-TOF: Systematic analyses of standards, catalyzed smoke analogs, meteorites, and Mars analogs in collaboration with Theme 3 and 4 team.

• Identify overlapping or related detections w/LDMS and GCMS

• Feed LDMS detections back to analog definition/analysis

• Complete “Tower TOF” instrument and begin calibration and demonstration runs with blanks and standards

• Addition of negative ion detection mode (3 instruments)

• Set up LD-EPI-MS on DS-TOF

• Set up postionization mode on Tower TOF

• Fine scale chemical imaging LDMS campaigns


Electron ionization TOF-MS

• miniature EI source developed at Goddard for APL TOF-MS, permits EI and LD-EPI

• Analyze more volatile high mass organics


Post-ionization system for REMPI/RIMS (in development)• Two-laser (Nd:YAG/OPO) LD-LPI-TOF-MS system (235 – 700 nm)• Online switch between lateral LPI (a) and coaxial LPI or resonant LD (b)

(a)

(b)


Backup Slides


An exobiology digression

• Current exobiology grant at APL: Organic Synthesis in Hypervelocity Impacts (OSHI)

• Developed specialized instrumentation using planetary major equipment (PME) grant

• Using laser mass spectrometry to probe formation of organics in post-impact plasma plumes (v > 25 km s-1)

• TOF-MS able to distinguish plume-formed from surface desorbed molecules via kinetic energy distributions and other factors. Extensive hydrocarbon formation occurs.

• Addresses entire spectrum from survival through complete molecular dissociation and recondensation in impacts.


An exobiology digression

The Hypervelocity Impact Simulation Microprobe (HISM) is used to generate laser mass spectra that simulate dust and micrometeorite impacts over a range of velocities, impactor diameters, and compositions.

Mass Spectrometer

Target Probe

Laser Power Supply

Laser Head

Main Laser Objective

HISM Electronics

Intact Survival

Complete Atomization

0 1 2 5 10 20 50 100

Depending on Angle, Composition, Mass

Impact Velocity (km s-1)

Molecular Fragmentation

Recombination of Fragments?

0 ? ~ 108 109 1010

ε (W cm-2)

No Plasma PlasmaLase

rIm

pact

Intact Survival

Complete Atomization

0 1 2 5 10 20 50 100

Depending on Angle, Composition, Mass

Impact Velocity (km s-1)

Molecular Fragmentation

Recombination of Fragments?

0 ? ~ 108 109 1010

ε (W cm-2)

No Plasma PlasmaLase

rIm

pact

Qualitative correlations between impact velocity and molecular survivability (top), and laser irradiance and processes (bottom).

Example HISM spectrum from simulated impact involving high-purity carbon and NH4NO3 target materials in a physical mixture. > 1.5 GW cm-2


Cation Ratio (Given)

10-4 10-3 10-2 10-1 100 101

Cat

ion

Ra

tio (

Mea

sure

d)

10-6

10-5

10-4

10-3

10-2

10-1

100

101

102

103

Powder/SiPellet/SiGlass/Siy = xPowder/FePellet/FeGlass/Fe

O

[Si]

Al

FeCa

Mg

Na

P

K/Ca

Ca

[Fe]

Ti

Mn

V

CrCuNi

Zn

Co

100x

1x

0.01x

Cs...Nd

Rb...Nb

Fe

Fe

O

O

Ca

Ca

Glass

Powder

Pellet

BHVO-2 Basalt Standard


JSC Mars-1 Simulant



High-resolution in situ chemical imaging

• xyz sample manipulation system developed in collaboration with Honeybee Robotics

• examine location of organics in meteorites

Other Honeybee Robotics Collaborations

• MSL Sample Acquisition/Sample Handling and Processing (SA/SPaH) system

• Precision subsampling systems

Sample Handling and Vacuum Stuff

Vacuum Issues (Mars)

• Method 1: (“brute force”) Acquire samples; use vacuum seals/valves; pump out.

• Method 2: (“relax requirements”) Sample and/or ionize at ambient pressure; draw into dynamically-pumped MS; consider designs that tolerate higher operating pressure.

• Evaluating current generation of Creare mini TMD pumps (to be flown in SAM on MSL)

Documents

Progress in Laser Desorption Mass Spectrometry: Sample Analysis in the Lab and in Space